RESPIRATION, AND ITS EFFECTS. 61 



"wliich we have spoken of in the blood, it rushes into the 

 heart when the chest is expanded, and when from any cause 

 respiration is delayed, the pulse becomes less frequent and more 

 languid, in consequence of the obstruction in the current of the 

 blood. Thus in violent fits of coughing, the chest collapses, the 

 air is expelled, and the blood, not being purified, is unfit for cir- 

 culation ; and the consequence is, the veins of the head become 

 distended, and in man the person becomes red or black in the 

 face, and sometimes a blood vessel has ruptured, and death 

 supervened. 



The Production of Animal Heat. — This important operation is 

 effected by means of respiration, — the chemical process carried 

 on in the lung's. 



The sensation of heat is derived from the presence of an ex- 

 tremely subtle fluid, called caloric, the particles of which have a 

 tendency to repel each other, and unite with other substances. 

 Thus if we touch a body whose temperature is lower than that 

 of our hand, caloric passes from the hand to this substance, and 

 the sensation of cold is experienced ; and if, on the other hand, the 

 temperature of the substance is higher, we feel a degree of heat 

 from the passage of caloric into the hand. It is a singular fact, 

 that this caloric may exist in two different states, the one in a 

 free or sensible form, the other in a latent or combined form. 

 Thus two substances may appear to be of the same temperature, 

 and yet one may contain a much greater degree of caloric than 

 the other, but so combined with tlie substance that it is not 

 sensible to the touch. If, however, the object be exposed to 

 the influence of some chemical agent, its latent caloric may be 

 set free or rendered sensible. For instance, if sulphuric acid 

 and water be mixed together, although each fluid were before 

 cold, the mixture is raised to a high temperature, and caloric is 

 evolved. In the fermentation of malt liquors the temperature of 

 the liquid is raised Avith the process, and carbonic acid is pro- 

 duced. And it is found that whenever this gas is evolved, that 

 caloric is produced and rendered sensible : thus in the lungs, 

 the oxygen of the atmosphere combines with the carbon of the 

 blood, and carbonic acid is produced as in fermentation. What 

 becomes then of this caloric ? One portion is expired in a sensible 

 form with the breath, which is thus rendered hotter and conse- 

 quently lighter, and thereby ascends : another portion becomes 

 sensible in the blood, and raises its temperature two degrees ; but 

 by far the greater portion of caloric is acquired by the arterial 

 blood, and there remains in a latent form. Some substances 

 have a much greater capacity for caloric than others : thus arterial 

 blood has more than venous blood : this being the case, as the 

 blood loses its arterial character in the course of circulation, 

 it loses also its capacity for retaining caloric ; and as the blood 



